The following patents are the prior art closest to the present invention known to the inventor:
U.S. Pat. No. 185,116--Mann PA1 U.S. Pat. No. 419,908--Bagley PA1 U.S. Pat. No. 1,966,359--Ryan PA1 U.S. Pat. No. 3,899,418--Lawrence
All of the enumerated patents disclose structures for separating heavy precious metals such as gold from an aqueous placer material. Mann and Bagley disclose mining riffles for arresting and retaining particles of gold, amalgam, quicksilver and the like. The Mann and Bagley devices, however, are bulky and awkward and do not readily lend themselves to pan mining ordinarily done by one person. The Ryan pan employs a plurality of riffles in the rim structure. The miner's pan of Lawrence includes a mineral trap depending from the center of the bottom of the pan as well as a separating groove. These patents do not teach the use of a trough in association with a pan, the trough having therein a ladder-like structure. The prior art merely teaches minor improvements in retrieving precious metals from a placer material, but does not indicate any means whereby one prospector can increase the rate of separation of heavy metal from residue while simultaneously trapping the metal particles.